If f (x) = 5x - 3, then what is f-1 (x) ?

I assume the question is: what is the inverse of f (x) = 5x - 3?

Change the f (x) into a y.

y = 5x - 3

Swap the y and x.

x = 5y - 3

Solve for y.

x + 3 = 5y

(x + 3) / 5 = 5y/5

x/5 + 3/5 = y

Finding the inverse of an equation is as simple as replacing the f (x) with y, swapping the y and x, and solving for y. When graphed, the resulting function is an exact mirror of the original function (it is mirrored across an invisible axis).